1. Field of the Invention
The specification relates to systems and methods for detecting pressure. In particular, the specification relates to systems and methods for implementing a wide-area sensor to detect pressure with reduced power consumption.
2. Description of the Background Art
Various types of sensors can be used to detect pressure on a surface including air pressure, resistive touch screens, micro-electro-mechanical system (MEMS) devices, strain gauges and membrane switches. A membrane switch is closed when pressure is applied to the switch. A membrane switch is open when pressure is released from the switch. These types of membrane switches are inexpensive and have a high reliability of usage (e.g., one million presses in a switch's life time).
Membrane switches are commonly used in keyboards. Applications of membrane switches in areas larger than keyboards include determining the mass of a person sitting in a car seat, and implementing a wide-area mat placed beneath a mattress, which can be used to detect if a person is lying on the mattress or not, etc. In these cases, the number of membrane switches included in the application is only a few but the application area is large. However, for applications using more membrane switches in a wide application area, high cost and high power consumption issues arise when connecting the membrane switches to a microcontroller that detects whether the membrane switches are closed or open.
For example, for a sensor with 18 rows×18 columns of membrane switches (e.g., 324 membrane switches in total), there are 36 signal lines required to connect to the microcontroller. A microcontroller having at least 36 general purpose input/output (GPIO) pins to satisfy this requirement (e.g., a microcontroller with 48 pins or 64 pins) can be very expensive. Furthermore, the only way to determine which switches are closed or open is to energize each row in turn and read each column for the row until all the rows are read, which is similar to traversing all the membrane switches one by one. It is time-consuming to read all the membrane switches in this approach. In an ultra-low power system, the amount of time taken to read all the membrane switches is a large power consumption penalty.